Chromium hydroxide green



Patented May 2, 1939 D UNITED STATES PATENT OFFICE CHROMIUM HYDRO-XIDE GREEN Albert Grasshoff, Hanover, and Wilhelm Kiinig, Stuttgart, Germany, assignors to G. Siegle & 00., G. in. b. H., Stuttgart, Germany No Drawing. Application July 29, 1936, Serial No. 93,228. In Germany August 2, 1935 18 Claims. (01. 134-58) It is known to manufacture the so-called tively wide limits and in general need only be Guignets green by heating alkali dichromate and relatively slight, for example only to 20 per boric acid and extracting with water (see in this cent., referred to dichromate. It depends more connection for example Rose, Mineralfarben particularly upon the nature of the additions em- 5 and Gentele, Lehrbuch der Farbenfabrikation). ployed in each case, as well as combinations 5 In practice it has been found that, by this procthereof, and the optimum conditions for each ess it is indeed possible to obtain a green color case may always be readily determined by small which may be employed as a coloring material, suitable preliminary tests. but when manufactured on a commercial scale, The additional substances according to the inthe products suffer from various disadvantages, vention are added to the reaction components and difficulties are encountered in the regular preferably in a fine state of division and manufacture, particularly with regard to the fact thoroughly intermingled, for example by first that the heated reaction mass tends to adhere mixing them intimately with one of the reaction by fusion to and cake on the furnace walls, and components and then uniting them with the other the nature of the products makes a sharp grindreaction component, or by intimately mixing 15 ing necessary. both together with the additional substances. I

In thecourse of exhaustive attempts to eliminate these disadvantages, the surprising discovery Examples has been made that it is possible in an extremely simple manner to obviate these difiiculties, and over and above that, even attain various special advantages by carrying out the known process for the manufacture of Guignets green in the presence of one or more reducing agents.

By working in this way according to the invention, very substantial improvements are secured both with regard to the manufacture and also in the nature of the end products. In the first place, the extremely troublesome adhesion for mp e It ay vary between 5.4 and 22 by fusion to or caking on the furnace bottom is gramsi Wlthout conslderajble qlfferences 30 obviated, and in addition a further preservation tamed the result- .Llliewlser the qualitlty of of the expensive furnace installations is also made born? acid be Vaned 1n accordance Wlth the possible by the fact that the temperature of calquallty deslred the end product' cination can be lowered considerably in compari- (2) In place of sulfur of portlon theFeOf, son with the method of Working usual heretofore. carbohydrate for example Potato p 15 In the second place, the product is obtained in a y whe eby corresponding alterations may form which renders unnecessary a further sharp be Obtained, the method being earned out in grinding, as has been necessary heretofore. other respects as in E D Q The y- A further surprising effe t of t present Procdrates may be added in quantitiesof for example ess finally resides in the fact that the additions 1030 grams- In the Case Of apartlal p c e 40 to be employed according to the invention prof the s f it is possible to p y for a p duce an alteration in tint, which is accompanied half Sulfur and half Starch additionbyanoteworthy improvement in the yield and in- (3) Products having a Special blue tinge are crease in the coloring power. obtained by adding, in place of elementary sulfur,

The reducing agents which come into considersodium thiosulfate, with or without the simul- 5 ation for the present process are advantageously taneous addition of one or more of the abovefor example elementary sulfur and/or suitable mentioned substances. Thus for example it is sulfur compounds, such as for example thiosulpossible to employ 250 grams of sodium chromate,

(1) grams of dichromate, 11 grams of 20 sulphur and 300 grams of boric acid are heated for 1 hour at 600 to 620 C. After heating, the mixture while still hot is thrown into 2 liters of water, boiled for a short time, and further washed and dried in the usual manner. About 80 grams 25 of Guignets green are obtained.

In the scope of this method of working, the quantity of added sulfur may be higher or lower,

fate, thiourea, polysulfides and the like. 750 grams of boric acid and grams of sodium 50 In place of or as well as sulfur-containing addithiosulfate. 50 tions, it is furthermore possible to add carbohy- (4) Products having a pronounced blue tinge drates, such as starch, sawdust, dextrin or the are obtained for example by employing as addilike or other suitable reducing agents. ticn thiourea or polysulfide in the following pro- The quantity of the additions to be employed portions: 50 grams of sodium chromate, 55 according to the invention may fluctuate in relagrams of boric acid, 8 grams of thiourea. 55

We claim:

1. The herein described process for the manufacture of Guignets green, which process consists in heating alkali dichromate and boric acid in the presence of a reducing agent selected from the group consisting of carbohydrates, sulfur and reducing sulfur compounds.

2. The process for the manufacture of Guignets green, comprising reacting an alkali salt of chromic acid with boric acid in the presence of a reducing agent selected from the group consisting of carbohydrates, sulfur, and reducing sulfur compounds and lixiviating the product.

3. The process as set forth in claim 2, in which the reducing agent is used in the proportion of to 20 per cent of the alkali salt of chromic acid.

4. The process for the manufacture of Guignets green, comprising reacting an alkali dichromate with boric acid in the presence of a reducing mixture consisting of a carbohydrate and a reducing agent selected from the group consisting of sulfur and reducing sulfur compounds, and. lixiviating the product.

5. The process for the manufacture of Guignets green, which comprises heating a mixture of about 100 parts by weight of alkali dichromate, from 5 to 22 parts sulfur and about 300 parts boric acid for about I hour at 600 to 620 0., boiling the product with water, and washing and drying the product. V

6, The process for the manufacture of Guignets green having a bluish tinge, which comprises reacting about 250 parts by weight of sodium chromate, about'750 parts of boric acid and about 140 parts of sodium thiosulfate, and lixiviating, washing and drying the product.

'7. The process for the manufacture of Guignets green having a pronounced blue tinge, which comprises heating a mixture of about 50 parts by weight of sodium chromate, about 150 parts of boric acid and about 8 parts of thiourea, digesting the product in water, and washing and drying the product.

8. A process, as claimed in claim 1, in which sulfur is used as reducing agent.

9. A process, as claimed in claim 1, in which a reducing sulfur compound is used as reducing agent.

10. A process, as claimed in claim 1, in which the water soluble salt of thiosulfate is used as reducing agent.

11. A process, as claimed in claim 1, in which thiourea is used as reducing agent.

12. A process, as claimed in claim 1, in which the water soluble salt of a polysulfide is used as reducing agent.

13. A process, as claimed in claim 4, in which starch is used as carbohydrate.

14. A process, as claimed in claim 4, in which sawdust is used as carbohydrate.

15. A process, as claimed in claim 4, in which dextrin is used as carbohydrate.

16. A process, as claimed in claim 4, in which the water soluble salt of thiosulfate is used as. reducing sulfur compound.

17. A process, as claimed in claim 4, in which thiourea is used as reducing sulfur compound.

18. A process, as claimed in claim 4, in which the water soluble salt of a polysulfide is used as reducing sulfur compound.

ALBERT GRASSHOFF. WILHELM KONIG. 

